Constant at any given place, the value of g varies from object to object (e.g. Planets), and also with the distance from the centre of the object. The relationship between the two constants is: g = GM/r2 where r is the radius of separation between the masses' centers, and M is the mass of the primary body (e.g. A planet). At Earth's surface, the value of g = 9.8 metres per second per second (9.8m/s2). See also weight.